Thermal treatment chambers are used to process various materials to change their physical properties, usually by heating the material to temperatures up to several hundred degrees Celsius. Typically, batches of several production units are loaded into the chamber and subjected to chamber temperatures for a fixed period of time.
Often it is desirable to test the temperature uniformity within a chamber, e.g. to ensure that the different production units in the same heating batch are receiving the desired heat treatment, or alternatively where only one production unit is treated at a time, to ensure the unit is exposed to a uniform temperature profile. One way this has been done is by placing a number of thermocouples at various locations within the chamber, and then monitoring the temperatures at these locations via electrical signals from the thermocouples.
One difficulty with this technique is that it can be difficult and dangerous to place the thermocouples when the chamber is at its operating temperature, particularly where the operating temperature is several hundred degrees Celsius. Furthermore, it takes at least a few minutes to place the thermocouples with sufficient accuracy to make repeatable and useful measurements, but a technician placing thermocouples in, for example, the searing heat used for heat treating, is unlikely to have sufficient time to make accurate placements.
Thus, greater accuracy and safety can be achieved by placing the thermocouples while the chamber is at room temperature. However, doing so can add significantly to downtime, because chambers often take hours to achieve operating temperature.
One possible solution is to temporarily attach the thermocouples to one of the production units being treated, before inserting the production unit in the chamber (or perhaps to permanently attach thermocouples to a "dummy" production unit). This technique increases safety and reduces downtime because the thermocouples can be inserted into the chamber as part of the normal production routine. However, because the thermocouples are attached to the production material, they often are not placed at the ideal locations for measurements and also are subject to placement inaccuracy. Furthermore, because the thermocouples are mounted on production material which typically has a large heat capacity, the readings obtained from the thermocouples are influenced by the production material and therefore are relatively less responsive to chamber temperature variations than thermocouples which are placed separately.
Optical pyrometers are in some cases used to perform localized temperature measurements in a thermal treatment chamber. The pyrometer is mounted at the end of a probe which is manually aimed at the desired location within the chamber. This technique has the disadvantage that the pyrometer is difficult to position accurately and consistently, and the chamber door must remain at least partially open to permit manual manipulation of the probe, potentially causing inaccurate readings.